Music sound systems for background coverage are well known, and have been used in public places such as restaurants and retail stores, as well as other locations, for a number of years. Such background music sound systems use compilations of re-recorded musical compositions, as opposed to original recordings, and provide low level background music which is low fidelity and somewhat innocuous. Such systems typically include a plurality of ceiling speakers with a "constant voltage" (usually 70 volts or 25 volts) distribution system, with transformers at each speaker for impedance matching. Signal sources for such background systems include radio subcarrier and telephone lines, both with limited bandwidth.
In such background systems, the low fidelity of the sound system was tolerable because of the limited purpose of the background music. However, the desire for better sound, which is particularly important when the program includes original musical recordings, with high quality instrumentals and vocals, began to change the composition of such systems. Thus, higher quality speakers were introduced and higher quality/high cost transformers were used to overcome some of the bandwidth limitations of the background type system transformers previously used. Additional speakers were added to the system to provide better coverage. However, such improvements added significantly to the cost of the sound system, and installation costs were significantly increased as well.
In a further development, bookshelf speakers having good frequency response replaced the ceiling speakers. Bookshelf type speakers are more expensive, but reduced the total number of speakers necessary because of their inherent broad horizontal coverage, which creates a pleasant ambient sound coverage with good bass response and adequate sound level. In some systems, bookshelf speakers are used in combination with ceiling speakers.
At the same time, high fidelity cartridge tape player systems were developed for program material extending for four hours or more. Extended play "programs" with a common theme comprising a series of original musical recordings then became available. The cartridge tape systems are desirable because they do not require any operator supervision and accordingly, the number of potential applications of such systems has increased significantly.
Such music sound systems became known as "foreground" music systems, connoting a higher quality sound using original recordings which is used to create an ambience, i.e. an atmosphere, which so-called background music systems could not. Such foreground systems have been installed successfully in many locations, particularly restaurants.
The disadvantages of previous foreground systems include increased cost of the components of the system, particularly the speakers and the transformers, increased cost of installation, and physical installation limitations because of the size and configuration of the bookshelf speakers and their associated transformers. Many potential applications, such as office space, grocery stores, and department stores, have been heretofore essentially excluded from using foreground music systems because of such limitations.
Still further, even such improved systems often lacked a full frequency response and frequently did not achieve uniform sound levels and desired overlap coverage throughout the entire area to be covered, due to the difficulty in achieving proper placement of the bookshelf speakers. Related to this problem is the matter of reverberation, which can be a significant problem in some acoustic environments, causing the music to become unintelligible or even annoying. The high cost of increasing the number of speakers and the lack of proper locations for the speakers even if cost were not an issue frequently prevent adequate solution to these problems.
A related problem with such systems concerns the use of a microphone for paging in the same sound system. The microphone volume is often difficult and/or inconvenient to control, both alone and relative to the music volume, and this often results in a page being difficult to hear, particularly as the ambient noise in the area increases. Distortion of the microphone sound also results with existing systems, because of overload.
The present invention, in attempting to solve the above problems and disadvantages, uses a complimentary array of microspeakers and bookshelf speakers to provide full sound coverage with good frequency response, driven by a current amplification circuit which provides the amplification necessary as well as an impedance match with the speakers, thereby eliminating the speaker transformers.